During the twentieth century, the drowning of Welsh valleys to supply
water for English cities became a contentious subject which led to non-violent
and violent campaigns and protests.

Llyn Llawddyn was the first reservoir in Wales. It was built in the
1880s and at the time it was the biggest man-made lake in the world.
In the 1890s, the City of Birmingham Corporation bought 180km² of land
in the Elan and Claerwen valleys in Powys. There was a great demand
for water in Birmingham for public health reasons and for industry.

In 1904 the Elan reservoir was opened by Edward VII and Queen Alexandra
to supply water for the City of Birmingham. Three dams were opened there
- Craig Goch, Pen y Garreg and Caban Coch, with a surface of 500 acres.

In 1907 Birkenhead town corporation created Alwen lake on the Hiraethog
mountain which supplied 9 million tons of water per day to the Wirral
Water Board. In 1923 the Corporation of Warrington attempted to drown
the Ceiriog valley, near Wrexham, but the measure was opposed because
the Welsh Members of Parliament voted against it.

Three dams were designed for Claerwen, but only one was built, between
1946 and 1953. The area was leased by the Midlands for 999 years for
a sum of 5 pence a year. It provided 75 tonnes of water per day.

Valuable natural resources were being taken from Wales without compensation
in many cases, and there was a growing feeling of discontent because
England was not exploiting her own resources to obtain water. During
the 1970s the river Trent, the third biggest river in England and Wales,
produced over 1,400 tonnes of water per day, but no reservoirs were
built there.

On occasions land in rural Wales was bought by English
cities through compulsory purchase and there was little that local people
could do to prevent this. As occurred in Tryweryn and Clywedog, Welsh
communities were destroyed when the valleys were drowned.

During the 1960s the concept of establishing a Welsh Water
Board was promoted. In 1971 a special report by the Council for Wales
called for a Water Development Authority in Wales to regulate the water
supply and to protect the interests of Wales. In 1971, Edward Heath's
Conservative government, with Peter Thomas as Secretary of State for
Wales, agreed to establish a Welsh Water Authority.